Blister Beetles in Soybean
Crop Damage: Blister beetles (Epicauta spp.) can be found throughout the U.S. and southern Canada. Adults are best known for producing a toxic chemical, cantharidin, which they secrete as a defense mechanism. While blister beetle toxicity to livestock is the primary concern, these insects can also cause severe defoliation in soybean.
Blister beetles feeding on soybean leaf.
Adam Sisson, Iowa State University
Pest Description: Adult beetles are slender, measuring ½ to 1 inch long, and may be ash gray, solid brown, solid black, or black with orange stripes. The segment between the head and abdomen (thorax) is narrow. Their wing covers are rounded at the tips and do not completely cover the end of the abdomen.
Blister beetle adult. The orange arrow indicates the narrow thorax. The blue arrow shows the wing covers that do not cover the abdomen.
Ashley Dean, Iowa State University
Blister beetle adult. The orange arrow indicates the narrow thorax. The blue arrow shows the wing covers that do not cover the abdomen.
Adam Sisson, Iowa State University
Scouting: Closely monitor soybean fields with a history of blister beetle infestations or those located near alfalfa fields. Adults are most active in the early morning and late afternoon and may gather in clusters. Estimate defoliation across the entire field, and use the Crop Protection Network’s Insect Defoliation Tool to accurately assess defoliation levels.
Management: There are no specific thresholds established for blister beetles in soybean. However, the standard soybean defoliation treatment thresholds apply – 30% during vegetative stages and 20% during reproductive stages. If beetles are clustered in certain areas, spot treatments may be warranted. Consider additional management measures if other defoliating insects are present.
Developed and reviewed by Carol Pilcher, Iowa State University and Robert Wright, University of Nebraska-Lincoln, with support from the United Soybean Board.
Blister beetles feeding on soybean leaf. Image by Adam Sisson, Iowa State University.
Blister beetle adult. The orange arrow indicates the narrow thorax. The blue arrow shows the wing covers that do not cover the abdomen. Image by Ashley Dean, Iowa State University.
A blister beetle adult on a leaf. The orange arrow indicates the narrow thorax. The blue arrow shows the wing covers that do not cover the abdomen. Image by Adam Sisson, Iowa State University.
Gallery images by Ashley Dean, Iowa State University and Adam Sisson, Iowa State University.
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